Method for improving safety of voltage regulator

ABSTRACT

A method for improving safety of voltage regulator is disclosed. In order to improve safety of a voltage regulator, a MOS-FET is disposed on a source power lane that receives power supplied from a DC power supply. A set of voltage regulators is connected to a set of fork power lanes, correspondingly, branching off from the source power lane. PTC thermistors are disposed on a surface or in the vicinity of semiconductor chips of the voltage regulators. When temperature at any one of the PTC thermistors increases, a protection controller turns off the MOS-FET. When temperature detected by a temperature sensor incorporated within the semiconductor chip has increased, each of the voltage regulators turns off the MOS-FET via a base management controller.

PRIORITY CLAIM

The present application claims benefit of priority under 35 U.S.C. §§120, 365 to the previously filed Japanese Patent Application No. JP2014-122932 with a priority date of Jun. 14, 2014, which is incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to voltage regulators in general, and particularly to a method for improving the safety of a voltage regulator having a switching element, and to a method for preventing smoking and burning of a switching element.

2. Description of Related Art

FIG. 7 describes the outline of a typical power-supply system used for a server. A power-supply unit (PSU) 501 supplies power to a group of sub-systems 503 to 507 making up a server with DC voltage. Each sub-system 503 to 507 is mainly made up of voltage regulators (VRs) 511 a to 511 c that convert the output voltage of the PSU 501 to predetermined voltage and loads 513 a to 513 c corresponding to the VRs, such as a central processing unit (CPU), a memory, and a hard disk drive (HDD). The VRs 511 a to 511 c are provided with fuses 509 a to 509 c, respectively, on the primary side. The sub-system 503 is configured so that, even when power supplied to any one of the loads 513 a to 513 c stops, the function of the sub-system does not stop completely as long as power is supplied to other loads.

A conventional DC power-supply apparatus including a switching element is configured to protect the circuit by turning the switching element OFF when the load generates a short-circuit failure. The switching element can function as the protection switch against a short-circuit failure only when such a switching element normally operates. Since switching elements are manufactured with a relatively high level of reliability, and so cause less failure in general, such a protective idea may not have a problem in that sense.

In the power-supply system of FIG. 7, if the switching elements in the to close state of the VRs 511 a to 511 c fail and so short-circuit current flow, the fuses 509 a to 509 c on the primary side can be molten so as to interrupt the related system only. Since the fuses 509 a to 509 c do not require a control circuit and are inexpensive, such a protective idea is rational for the failure of a switching element that hardly causes a failure.

In the power-supply system of FIG. 7; however, the VRs 511 a to 511 c may cause smoking and burning. Investigations on such a phenomenon show that a switching element burns severely. A direct cause of the burning of a switching element results from the element generating a large amount of heat due to large current. If a switching element in the close state fails, short-circuit current flowing will cause burnout of any one of the fuses 509 a to 509 c. However, smoking or burning generated means that the fuses 509 a to 509 c do not melt, or the timing of the melting, if any, may not work together with the circuit.

The fuses 509 a to 509 c have to have elements that is not degraded due to repeated inrush current when energization starts at the VRs 511 a to 511 c, and since they are disposed to protect the circuit from short-circuit, its blowout current is quite larger than the rated current of the VRs 511 a to 511 c, and its pre-arcing time also has to be longer. In one example, the fuses 509 a to 509 c have current-time characteristics such that it takes two minutes to cause a blowout when current twice of the rated current of the VRs 511 a to 511 c flows. Such a current value and energizing time are sufficient to cause smoking and burning at the switching elements.

If a switching element whose resistance is close to zero causes a short-circuit failure (this is called dead short-circuit), the pre-arcing time is short in spite of a large current value, and so the fuses 509 a to 509 c can be molten prior to smoking and burning so as to interrupt the circuit. Recent studies show that, however, if the switching element having some resistance causes a short-circuit failure (this is called resistance short-circuit), the switching element causes smoking and burning to interrupt the circuit before burnout of the fuses 509 a to 509 c or without causing a burnout of the fuses 509 a to 509 c.

Switching elements are degraded over time because they frequently turn ON/OFF. If a switching element burns while generating heat severely, all of the devices around it may be damaged or a normal sub-system also has to be replaced in some cases. Further, if a switching element generates heat, it causes the risk of fire, and so it is not favorable to leave such a situation unsolved even when the risk is small. The PSU 501 has to supply power to each sub-system 503 to 507, and so has large rated current compared with the VRs 511 a to 511 c, and so the protection circuit thereof also cannot prevent smoking and burning when resistance short-circuit occurs at the switching element.

Another problem occurs, which results from the loads 513 a to 513 c including a device that receives power from VRs 511 a to 511 c. For instance, when the load 513 b includes a device receiving power from the VR 511 a as well, and if the fuse 509 a is molten, the device receives power continuously from the VR 511 b in spite of stopping of the power-supply from the VR 511 a. Then the device of the load 513 b generates latch up, which increases the risk leading to secondarily generated smoking and burning.

Consequently, it would be desirable to provide a power-supply system having improved safety against resistance short-circuit of a switching element.

SUMMARY OF THE INVENTION

In accordance with a preferred embodiment of the present invention, a power-supply system includes a protection switch disposed on a power lane receiving power supply from a DC power supply, a group of voltage regulators, each having a switching element and branching off from the power lane, a temperature sensor for detecting temperature of the voltage regulators, and a controller for turning the protection switch OFF when temperature at any one of the voltage regulators increases and stops power supplied to the group of voltage regulators. With this configuration, if the switching element fails due to resistance short-circuit, the protection switch can be turned OFF in response to the detection of temperature such that smoking and burning can be prevented.

When the switching element is incorporated into a semiconductor chip, the temperature sensor can detect temperature at a surface or vicinity of the semiconductor chip. Temperature is detected from the outside of the semiconductor chip, whereby the temperature sensor is not affected from a sudden increase in temperature, if any, and can turn the protection switch OFF reliably. The temperature sensor may include a PTC thermistor. When temperature detected by the temperature sensor incorporated in the semiconductor chip increases, the controller can turn the protection switch OFF.

A temperature sensor for detecting temperature outside of the semiconductor chip, and a temperature sensor for detecting temperature inside thereof are provided, whereby reliable protection can be provided even when the switching element generates heat suddenly. When ON resistance or OFF resistance of the switching elements calculated from voltage and current increases, the voltage regulators may send a signal to turn the protection switch OFF to the controller. The present invention is suitable for the case where the group of voltage regulators include a first voltage regulator and a second voltage regulator that output mutually different voltages, and loads of the voltage regulators include a device that operates with output voltage from the first voltage regulator and output voltage from the second voltage regulator. With this configuration, if abnormality occurs at any one of the voltage regulators, all of the voltage regulators stop, and so latch up of the device as a load can be prevented.

All features and advantages of the present disclosure will become apparent in the following detailed written description.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure itself, as well as a preferred mode of use, further objects, and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:

FIGS. 1A-1B are diagrams of a blade server;

FIG. 2 is a block diagram of the blade server from FIG. 1;

FIG. 3 is a block diagram of the sub-systems within a server unit of the blade server from FIG. 1;

FIG. 4 is a schematic diagram of a main sub-system within one of the sub-systems from FIG. 3;

FIG. 5 is a schematic diagram of a voltage regulator;

FIG. 6 is a flow diagram describing the operation of the power-supply system; and

FIG. 7 is a block diagram of a typical power-supply system used for a server.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

A power-supply system according to the present invention preferably is applicable to a set-type computer system. A set-type computer system includes a group of computer units, each having an equivalent computer function. Each computer unit includes hardware such as a processor, a system memory, an input/output (I/O) controller, a memory and a peripheral device, and software such as an operating system and an application program.

Each computer unit receives power from a power-supply unit (PSU) that converts utility power to DC voltage. Only one PSU may be provided for the computer system, or one PSU may be provided for a group of a plurality of computer units. Each computer unit includes a group of sub-systems. Each sub-system includes a group of voltage regulators (VRs). The set-type computer system may be implemented as a rack-mountable server, a blade server, a router or the like.

FIGS. 1 to 3 describe the outline of a blade server 10. FIG. 1A illustrates the outside shape of the blade server 10, and FIG. 1B illustrates the internal configuration. FIG. 2 illustrates the outline of a power-supply system including a PSU 21 and server units 100 a to 100 h, and FIG. 3 is a block diagram of a group of sub-systems making up the server unit 100 a.

In FIG. 1A, a rack 11 includes a front panel 23 on the surface, and internally accommodates the plurality of server units 100 a to 100 h, a midplane 13, a switch module 15, a chassis management module (CMM) 17, a fan module 19 and the PSU 21. Each server unit 100 a to 100 h includes a mother-board in an independent enclosure, and internally includes hardware and software resources to operate as an independent computer.

The midplane 13 is a circuit board including wiring for signals and power and connectors on both faces for coupling with the modules. The server unit 100 a to 100 h can connect to the midplane 13 that is energized with the output voltage from the PSU 21 in a hot-swap manner. The switch module 15 includes a group of switches for connection to a network or an external memory. The CMM 17 is to inform the operating state of the blade server 10 to a distance or to display it on the front panel 23. The fan module 19 dissipates heat inside of the rack 11. The PSU 21 converts AC voltage to DC voltage, and supplies power to the server units 100 a to 100 h and other modules.

In FIG. 2, the server units 100 a to 100 h are connected to the midplane 13 at their power terminals 105 a to 105 h and signal terminals 107 a to 107 h. Then the PSU 21 and the CMM 17 are connected to the midplane 13. The CMM 17 is connected to the front panel 23. The PSU 21 supplies power to each server unit 100 a to 100 h via the midplane 13 and the power terminals 105 a to 105 h.

In FIG. 3, at the power terminal 105 a of the server unit 100 a, source power lanes 234 a to 234 c are connected to a route power lane 106 a. The source power lanes 234 a and 234 b are connected to main sub-systems 151 a and 151 b, respectively, and the source power lane 234 c is connected to a common sub-system 151 c. Herein the route power lane 106 a corresponds to a circuit that supplies power from the PSU 21 to the three sub-systems 151 a to 151 c, and the source power lanes 234 a to 234 c correspond to a circuit that supplies power to the three sub-systems 151 a to 151 c.

The main sub-systems 151 a and 151 b each include a CPU and a system memory, and operate mutually independently. The common sub-system 151 c includes an I/O controller and a HDD that both or one of the main sub-systems 151 a and 151 b have to use to function as a computer, and does not function independently. In the application of the present invention, the number of the main sub-systems 151 a and 151 b may be one or more. The function of the common sub-system 151 c may be incorporated into each main sub-system 151 a or 151 b and be omitted. The sub-systems 151 a to 151 c include MOS-FETs 235 a to 235 c for protection, base management controllers (BMC) 203 a to 203 c, VRs 205 a to 209 a, 205 b to 209 b, and 205 c to 209 c, respectively.

The VRs are switching regulators to convert output voltage from the PSU 21 to predetermined stable voltage in accordance with the load. The VRs 205 a to 209 a supply power to loads 211 a to 215 a, such as a CPU and a system memory, the VRs 205 b to 209 b supply power to loads 211 b to 215 b, such as a CPU and a system memory, and the VRs 205 c to 209 c supply power to loads 211 c to 215 c, such as a HDD and an I/O controller. The BMCs 203 a to 203 c inform the CMM 17 of the operating state of the sub-systems 151 a to 151 c via the signal terminal 105 b, and control the MOS-FETs 235 a to 235 c.

FIG. 4 is a schematic diagram describing the circuit configuration of the main sub-system 151 a. The PSU 21 supplies power to an input terminal VIN on the source power lane 234 a via the route power lane 106 a. The input terminal VIN is connected in series with a current sense resistor 233 a and an n-type MOS-FET 235 a. The current sense resistor 233 a has both ends connected to a protection controller 201 a. The MOS-FET 235 a has a gate connected to the protection controller 201 a. Fork power lanes 204 a to 204 c branch off from the MOS-FET 235 a, to each of which the VR 205 a to 209 a is connected.

The fork power lanes 204 a to 204 c correspond to a circuit that supplies power to their corresponding VRs 205 a to 209 a. The VRs 205 a to 209 a output stable and predetermined voltage V21, V22 and V23, respectively, for use at their corresponding loads 211 a to 215 a. The VR 205 a supplies power to the load 211 a mainly including a CPU, the VR 207 a supplies power to the load 213 a mainly including a system memory, and the VR 209 a supplies power to the load 215 a including another device.

Some devices included in the loads 211 a to 215 a operate with voltage output from another VR and with a plurality of voltages. The input terminal VIN is connected to the ground via a resistor 236 a and Positive Temperature Coefficient (PTC) thermistors 351 a to 355 a connected in series. The PTC thermistors 351 a to 355 a are elements having flat temperature-resistor characteristics at normal temperatures, but suddenly increasing in resistance when the temperature exceeds a certain level (Curie temperature).

The PTC thermistors 351 a to 355 a are disposed so as to measure temperature at the surface or environmental temperature in the vicinity of a semiconductor chip of a switching circuit 303 (FIG. 5) making up the VR 205 a to 209 a. A n-type MOS-FET 231 a has a gate connected to a connecting point of the resistor 236 a and the PTC thermistor 351 a, a drain connected to a terminal 202 a of the protection controller 201 a, and a source connected to the ground. The drain of the MOS-FET 231 a is connected to a connecting point between voltage-dividing resistors 237 a and 239 a connected in series between the input terminal VIN and the ground.

The drain of the MOS-FET 231 a is connected to drains of n-type MOS-FETs 251 a and 253 a that are connected in parallel. The MOS-FETs 251 a and 253 a have sources connected to the ground. The MOS-FET 251 a has a gate connected to the BMC 203 a. The MOS-FET 253 a has a gate connected to the BMC 203 c included in the common sub-system 151 c.

A power-supply terminal VCC supplies power for driving of the protection controller 201 a, the VRs 205 a to 209 a and the BMC 203 a. The main sub-system 151 b also has a similar configuration, and the common sub-system 151 c is different in that it does not include a MOS-FET corresponding to the MOS-FET 253 a that operates with a signal of the BMC 203 a, 203 b of another main sub-system 151 a, 151 b.

FIG. 5 is a schematic diagram describing the circuit configuration of the VR 205 a. Although the VR 205 a actually includes still more elements, FIG. 5 illustrates the elements in the range required for understanding of the present invention. The VR 205 a mainly includes a PWM controller 301, a switching circuit 303 and a reactor 313. The switching circuit 303 is configured so as to include a driver circuit 305, n-type MOS-FETs 309 and 311, a temperature detection circuit 307 and the like incorporated into one semiconductor chip.

The driver circuit 305 receives a PWM signal from the PWM controller 301 and switching-controls the MOS-FETs 309 and 311 connected in series in the fork power lane 204 a in a synchronous rectification manner so as to convert input voltage V11 to stable output voltage V21 and outputs it to an output terminal VOUTr via a node 333 and the reactor 313. The driver circuit 305 includes an operational amplifier, and so measures current I11 flowing through the MOS-FET 311 that is calculated from the input voltage V11 at the node 331, the output voltage V21 at the node 333, the ON resistance of the MOS-FET 311 on the low side and the voltage at the node 333, output current I21 calculated from the resistance of the reactor 313 and the voltage at a capacitor 315, and the like.

The driver circuit 305 feedbacks the output voltage V21 at the node 333 to the PWM controller 301. Then the PWM controller 301 compares the fed-back voltage Vfb with set voltage to control the duty ratio of the PWM signal. If abnormality occurs in the input voltage V11, the output voltage V21, the current I21, I22 and the like, and if ON resistance or OFF resistance of the MOS-FETs 309 and 311 calculated from voltage and current changes by a preset value or more, the driver circuit 305 outputs an error signal to the PWM controller 301.

The temperature detection circuit 307 includes a temperature sensor incorporated into the semiconductor chip of the switching circuit 303, and if the internal temperature T1 of the semiconductor chip exceeds a predetermined value, then the temperature detection circuit sends an error signal to the PWM controller 301. Receiving an error signal from the driver circuit 305 or the temperature detection circuit 307, the PWM controller 301 outputs the error signal to the BMC 203 a. The error signal may be sent directly from the driver circuit 305 to the BMC 203 a by skipping the PWM controller 301.

The PTC thermistor 351 a is attached to the surface of the switching circuit 303 or the vicinity thereof, and is connected in series with other PTC thermistors 353 a and 355 a between the input terminal VIN (FIG. 4) of the source power lane 234 a and the ground in a circuit independent of the VR 205 a. The VRs 207 a and 209 a also may be configured similarly.

Note here that FIGS. 1 to 5 illustrate simplified configuration and connection relationship of major hardware relating to the present embodiment to describe the present embodiment. In order to make up a power-supply system, many other devices are used other than those described in the above. Since they are well-known for those skilled in the art, detailed descriptions thereon are omitted here. A group of blocks is illustrated in the drawing may be one integrated circuit or device, or conversely one block may be divided into a plurality of integrated circuits or devices, which also are included in the scope of the present invention as long as they are in the range where those skilled in the art can select freely.

Referring now to the flow diagram of FIG. 6, the operation of the power-supply system in FIGS. 4 and 5 is described below. The following mainly describes the operation of the main sub-system 151 a, and the operation of the main sub-system 151 b and the common sub-system 151 c also can be understood similarly. At block 401, the power terminal 105 a and the signal terminal 1056 of the server unit 100 a are connected to the midplane 13 in the energization state. Then the protection controller 201 a of the main sub-system 151 a is turned ON. At this time, the MOS-FETs 231 a, 251 a and 253 a are OFF.

When the protection controller 201 a detects input voltage VIN via the voltage-dividing resistors 237 and 239, the protection controller controls the gate voltage of the MOS-FET 235 a to suppress inrush current. When the inrush current disappears, the protection controller 201 a turns the MOS-FET 235 a ON completely. Subsequently at block 403, the Vas 205 a to 209 a start operation to supply power to the loads 211 a to 215 a.

At block 405, abnormality, such as increase in ON resistance or OFF resistance of the MOS-FETs 309, 311, occurs at the VR 205 a, which may be a sign of or lead to resistor short-circuit of the MOS-FET 309. At block 407, when the driver circuit 305 detects abnormality at the VR 205 a from the voltage V11, V21, the current I11, I21 and the like, then the driver circuit outputs an error signal, and the procedure proceeds to block 409. When the temperature detection circuit 307 detects abnormality at the internal temperature T1 as well, the temperature detection circuit outputs an error signal, and the procedure proceeds to block 409.

At block 409, when the PWM controller 301 receives an error signal from the driver circuit 305 or the temperature detection circuit 307, then the PWM controller outputs the error signal to the BMC 203 a, in response to the error signal, the BMC 203 a turns the MOS-FET 251 a ON. Then, the potential at the terminal 202 a drops, so that the protection controller 201 a turns the MOS-FET 235 a OFF, meaning that power-supply to all of the VRs 205 a to 209 a stops. The circuit in which the driver circuit 305 or the temperature detection circuit 307 outputs an error signal to turn the MOS-FET 235 a OFF is called a primary protection circuit.

When only the VR corresponding to the failure is stopped through blowout of the fuse as in the power-supply system of FIG. 7, latch up may occur at the load of the VR keeping the operation after the failure. On the other hand, in the present embodiment, latch up does not occur because all of the VRs 205 a to 209 a stop. Herein latch up is a phenomenon where parasitic transistor of a bipolar type that is formed at a CMOS-type integrated circuit (IC) turns a conductive state, and the IC causing latch up may be broken. The VRs 207 a, 209 a, the main sub-system 151 b and the common sub-system 151 c also operate similarly when abnormality occurs.

The primary protection circuit is effective for the case where the PWM controller 301 and the driver circuit 305 or the temperature detection circuit 307 can output an error signal. However, they may fail due to heat prior to output of an error signal. The primary protection circuit may be configured so as to send a signal directly from the driver circuit 305 or the temperature detection circuit 307 to the terminal 202 a of the protection controller 201 a by skipping the BMC 203 a.

At block 421, when the temperature at the PTC thermistor 351 a to detect temperature increases along with the operation of the primary protection circuit and exceeds the Curie temperature, then the resistance value suddenly increases. As a result, the MOS-FET 231 a turns ON because the gate voltage increases, meaning that the potential at the terminal 202 a decreases, and so the protection controller 201 a turns the MOS-FET 235 a OFF. At this time, the protection controller 201 a informs the BMC 203 a of stopping of power-supply to the source power lane 234 a. The MOS-FET 235 a turns OFF when the resistance of the PTC thermistors 353 a and 355 a corresponding to the VRs 207 a and 209 a increase as well.

The circuit where the PTC thermistors 351 a to 355 a turn the MOS-FET 235 a OFF is called a secondary protection circuit. The secondary protection circuit is a system independent of the switching circuit 303, the PWM controller 301 and the BMC 203 a making up the primary protection circuit, and so is not affected from the heat generated at the switching circuit 303. In this way, the secondary protection circuit can protect the circuit reliably even when the primary protection circuit does not function. If both of the primary protection circuit and the secondary protection circuit do not function, then the MOS-FET 309 will burn in time. Since the present embodiment has a double protection circuit, such risk is low.

If the primary protection circuit or the secondary protection circuit operates so as to stop the common sub-system 151 c, then the main sub-systems 151 a and 151 h cannot fulfill the function as the server unit 100. At block 411, when the common sub-system 151 c turns the MOS-FETs 235 a to 235 c for protection OFF, then the procedure proceeds to block 413. When a failure occurs at the VRs 205 c to 209 c, then the BMC 203 c in the common sub-system 151 c turns the MOS-FET 235 c OFF and at the same time turns the MOS-FETs 235 a and 235 b of the main sub-systems 151 a and 151 b OFF.

The main sub-systems 151 a and 151 b are configured so that only one of them can fulfill the function as the server unit 100 together with the common sub-system 151 c. That is, even when one of the main sub-systems 151 a, and 151 b turns the MOS-FETs 235 a and 235 b OFF, this does not stop the other main-sub system and the common sub-system 151 c.

At block 415, the BMC 203 a to 203 c that turns the MOS-FET 235 a to 235 c OFF informs the CMM 17 as such. Then the CMM 17 displays the error contents on the front panel 23. When the MOS-FET 235 a is turned OFF through the operation of the MOS-FETs 231 a, 251 a, and 253 a, the protection controller 201 a does not return the state unless the user resets manually, so as to ensure the security.

As has been described, the present disclosure provides a method for improving the safety of a voltage regulator having a switching element.

While the disclosure has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the disclosure. 

What is claimed is:
 1. A power-supply system comprising: a protection switch disposed on a power lane receiving power from a DC power supply; a plurality of voltage regulators, wherein at least one of said voltage regulators includes a switching element and branching off from said power lane; a temperature sensor for detecting temperature of said voltage regulators; and a controller for turning off said protection switch when temperature at any one of said voltage regulators has increased and for stopping power supplied to said plurality of voltage regulators.
 2. The power-supply system of claim 1, wherein said temperature sensor detects temperature of a semiconductor chip when said switching element is incorporated within said semiconductor chip.
 3. The power-supply system of claim 2, wherein said temperature sensor detects temperatures inside of said semiconductor chip.
 4. The power-supply system of claim 1, wherein said temperature sensor includes a FTC thermistor.
 5. The power-supply system of claim 1, wherein in response to an abnormality for ON/OFF resistances of said switching elements, said voltage regulators send a signal to turn off said protection switch to said controller.
 6. The power-supply system of claim 1, wherein said voltage regulators include a first voltage regulator and a second voltage regulator that output mutually different voltages, and loads of said voltage regulators include a device that operates with output voltage from said first voltage regulator and output voltage from said second voltage regulator.
 7. A sub-system for a computer comprising: a processor and a system memory; a protection switch disposed on a power lane receiving power from a DC power supply; a plurality of voltage regulators, wherein at least one of said voltage regulators includes a switching element to supply power to said processor and said system memory; a first temperature sensor for detecting temperature of said voltage regulators; and a first protection circuit for turning off said protection switch in response to a temperature at any of said voltage regulators has increased.
 8. The sub-system of claim 7, wherein said switching element is incorporated within a semiconductor chip, and said first protection circuit turns off said protection switch in response to a temperature of said semiconductor chip has increased.
 9. The sub-system of claim 8, further comprising: a second temperature sensor incorporated within said semiconductor chip; and a second protection circuit for turning off said protection switch in response to a temperature detected by said second temperature sensor has increased.
 10. A method for improving safety of a voltage regulator, said method comprising: providing a voltage regulator with a switching element at one of a plurality of fork power lanes branching off from a source power lane; detecting temperature at said switching element of one of said voltage regulators; and stopping power supplied from said source power lane in response to a temperature at any of said voltage regulators has increased.
 11. The method of claim 10, wherein said detecting temperature further includes detecting temperature of a semiconductor chip when said switching element is incorporated within said semiconductor chip.
 12. The method of claim 10, further comprising: in response to an abnormality occurs in ON resistance of said switching elements, stopping power supplied from said source power lane.
 13. The method of claim 10, further comprising: in response to an abnormality occurs in OFF resistance of said switching elements, stopping power supplied from said source power lane. 